Antispam, Amavisd & CPU

We've had Zimbra NE running for over a year now. We're very happy with it. Initially we did not enable anti-virus or anti-spam as we had a third party product.

We recently decided to turn on anti-spam only and ran into a serious problem. The amavisd daemon 100% flatlined the cpu on the mta's. It caused serious email delivery delays and thousands of messages in the deferred queue.